The present invention relates generally to apparatus and methods for mixing chemicals, and more specifically to apparatus and methods that minimize production of unwanted byproducts when mixing dilute concentrations of chemicals.
Stroma-free hemoglobin solution, commonly referred to as SFHS, has been extensively studied for use as a whole blood substitute. SFHS is produced by removing all cell membrane components (i.e., stroma) from outdated human red blood cells. SFHS has advantages over whole blood in that it does not require cross-matching for blood type and may be safely stored for long periods. Unfortunately, when free of the stroma, hemoglobin, the oxygen-carrying component of blood cells, binds oxygen so tightly that its use for oxygen transport is severely compromised. Additionally, stroma-free hemoglobin has a short intravascular retention time in animals due to its small molecular size.
The prior art has discovered that SFHS can be modified to decrease the oxygen affinity of the hemoglobin and to polymerize the hemoglobin molecules to increase their size. The most widely used modification to decrease oxygen affinity reacts the hemoglobin with pyridoxal-5'-phosphate (PLP), as described by Benesch et al., in Biochemistry, Vol. 11, 3576 (1972). The most widely used modification to polymerize SFHS reacts the hemoglobin with a bifunctional cross-linking reagent such as gluteraldexyde. Detailed descriptions of both the process of making SFHS from whole blood and the subsequent modification of SFHS may be found in U.S. Pat. No. 4,136,093 to Bonhard et al. and in U.S. Pat. No. 4,001,200 to Bonsen et al.
Unfortunately, prior art processes for producing modified SFHS have not produced a product substantially free from undesirable byproducts and have not prevented the SFHS from oxidizing and producing undesirable levels of methemoglobin, a form of hemoglobin unsuitable for carrying oxygen. Additionally, the resulting molecular weights and other physical properties of the modified SFHS produced by prior art processes indicate that the desired chemical reactions have not been well controlled.
Modification of SFHS calls for very dilute concentrations of reagent to be mixed with SFHS. Prior art processes typically directly mix reagents with the SFHS to be modified, followed by agitating or stirring. This direct mixing results in micro-concentrations of reagents which produce the undesirable byproducts. While the prior art has discovered methods of removing these antigenic elements, those methods are after-the-fact and reduce the efficiency of the process. Thus it is seen that there is a need in the art for an improved apparatus and method that produces modified SFHS from previously prepared SFHS with a minimum production of undesirable byproducts and methemoglobin.
It is, therefore, a principal object of the present invention to provide an apparatus and method for modifying SFHS that produces minimum concentrations of undesirable byproducts and methemoglobin.
It is another object of the present invention to provide an apparatus and method for modifying SFHS that allows controlled reaction conditions which produce an uniformly consistent solution over extended periods of time.
It is yet another object of the present invention to provide a generalized apparatus and method for reacting dilute concentrations of delicate bioorganics without creating micro-concentrations of reactant during the reaction process.
It is a feature of the present invention that it provides a method for preparing large volumes of modified SFHS suitable for transfusion. If modified SFHS is chosen as a whole blood substitute for use in on-site treatment of major battlefield injuries, such large quantities will become necessary.
It is another feature of the present invention that it can be easily modified to produce, for example, methemoglobin from modified SFHS, which can then be further concentrated for use as a treatment in cyanide poisoning.
It is an advantage of the present invention that it provides a closed-loop system providing protection from environmental contamination.
It is another advantage of the present invention that all reactant materials are utilized with little waste, and production time is half that of other methods in use.
It is yet another advantage of the present invention that the chemical reactions are well controlled, eliminating the need found in much of the prior art for additional chemicals to stop reactions, and allowing tailoring of the physical properties of the resulting product to meet varying needs.
These and other objects, features and advantages of the present invention will become apparent as the detailed description of certain representative embodiments proceeds.